Method and device for determining a misalignment of the radiation characteristic of a sensor for adjusting the speed and distance of a motor

ABSTRACT

A device and a method are for monitoring misalignment of a distance sensor on a vehicle which represents a combination of two individual procedures. The two individual procedures are selected in such a way that one procedure has advantages in areas in which the other procedure functions disadvantageously, so that the weaknesses of one procedure may be compensated for by the strengths of the other procedure. Furthermore, with the aid of this combination, it may be decided with far greater certainty whether a misalignment is present which may be removed using suitable correcting measures, or whether an extreme misalignment is present, based on which the system must be switched off.

FIELD OF THE INVENTION

The present invention relates to a method and a device for detectingand/or correcting misalignment of a distance sensor on a vehicle.

BACKGROUND INFORMATION

Some methods and devices for recognizing misalignment have been known tohave the function of being able to self-correct their sensor viewingzone.

German Published Patent Application No. 197 46 524 describes acompensation device for compensating for the installation tolerances ofa distance sensor in a vehicle. This is done by having the evaluationelectronics registering the object distances and the object angles ofthe detected objects. These data are averaged over a specifiably longtime, and-the thus ascertained object angle average is accepted as thenew nominal directional angle of the preceding vehicle. Furthermore, acorrecting angle is calculated from the difference of the nominaldirectional angle and the actual directional angle. The registeredobject angles are corrected with this difference angle.

European Published Patent Application No. 0 782 008 describes a devicefor calculating and correcting the deviation of the center axis of anobstacle recognition device on a vehicle and equipment forproximity-controlled cruise control based on a preceding vehicle. Thissystem recognizes standing objects, and from the positional displacementof the standing object relative to the sensor in time, it calculateswhether the standing object has a relative speed component which isorthogonal to the axis of symmetry of the sensor's viewing zone, alsocalled the optical axis. In the case of an accurately adjusted sensor, amean value generation in time of this lateral relative speed gives avalue tending to zero. In the case of a sensor's viewing zone that isout of alignment, a value not equal to zero is obtained by the meanvalue generation in time, which, by its magnitude permits drawing aconclusion on the misalignment angle of the sensor. Using this method, amisalignment of the sensor can be recognized, and the sensor'smisalignment can be corrected.

Both methods have a device and a method, respectively, for recognizingmisalignment, and both methods correct, upon recognizing misalignment,in such a way that a correcting angle ascertained from the measuredvalues is added to the measured object angle. The axis of symmetry ofthe sensor is tilted by calculation in such a way that it approximatelycoincides with the central axis of the vehicle.

SUMMARY

It is common to conventional methods and devices for recognizingmisalignment of distance sensors that in specified travel situationsthey yield good results, and in other travel situations they yieldresults the errors of which cannot be neglected. Thus, advantageous anddisadvantageous travel states exist for each system.

It is an object of the present invention to let two or more differentlydefined individual procedures for misalignment recognition proceedsimultaneously in combination and monitor the travel state or operate adevice which makes use of two or more individual procedures. These twoindividual procedures are developed in such a way that at least oneprocedure yields reliable values in each travel state. Thereby, theweakness of one procedure, namely that it yields unreliable values inthis travel state, is compensated for by the strength of another method,since the latter yields reliable values in this travel state. For theevaluation of the results of the individual procedures, a quality factoris developed from the currently present travel state for each individualprocedure, which are used for the weighting of the results of theindividual procedures. A linked misalignment value may be determined,depending on the weighted results of the individual procedures, as wellas the results of the value linkage, which is corrected as a function ofthese values, or as a result of which the system is switched off forsafety reasons. Defects in the sensor hardware become apparent fromerror images which may be represented by special misalignment vectors.Such a misalignment vector is made up of a linear combination of themisalignment values of the individual procedures. By monitoring theup-to-date-misalignment vectors, some hardware functions of the sensorimportant to the operation may thus be monitored. The present inventionis suitable for horizontal and also for vertical misalignmentrecognition and/or misalignment correction. In case a verticalmisalignment recognition and/or correction is to be performed, thesensor may also be in a position to measure the elevation angle ofreflecting objects.

If a travel situation occurs in which an individual procedure usedyields unreliable measured values, the results of this procedure areweighted more lightly at this point in time than another individualprocedure which is expected to yield more reliable values in this travelsituation, with the aid of a quality factor. By such a combination ofindividual procedures, it is possible to compensate for the weak pointsof one procedure by the strength of another procedure. It is alsopossible to predict with greater probability, from a measured sensormisalignment, that there is misalignment. If both procedures determinethat there is misalignment, but in different angular directions, thismay be caused by too large single procedure errors. If misalignmentvalues appear in the same angular direction and at approximately equalangles from the vehicle's center axis, one may assume with greaterprobability than when only one individual procedure is used, that thesensor's axis has been shifted. In this case, one may make a reliablecorrection or switch off the system at smaller misalignment values thanis possible using a individual procedure. In accordance with the presentinvention, operation of a proximity-controlled vehicle under cruisecontrol is much safer than operating a vehicle having a sensor which ismonitored by only one individual procedure for misalignment.Furthermore, the error due to disadvantageous surroundings is held muchsmaller than with an individual procedure, since at the time ofmeasuring, the more reliable procedure is treated as more dominantbecause of the lower weighting of the unreliable result.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of two vehicles traveling one behind the other inthe same lane, the following vehicle being provided with a deviceaccording to the present invention.

FIG. 2 is a diagram illustrating the shutoff range of the system as afunction of the two orthogonal individual procedures.

FIG. 3 is a block diagram of an example embodiment according to thepresent invention.

FIG. 4 is a block diagram of a second example embodiment according tothe present invention.

DETAILED DESCRIPTION

FIG. 1 illustrates a lane 1, on which two vehicles 2 and 3 are travelingone behind the other, such that vehicle 3 follows vehicle 2. Vehicle 3is equipped with a sensor 4 for speed control and proximity-controlledcruise control, which includes the present invention. Ray 8 representsthe center axis of vehicle 3, which, in the case of an accuratelyadjusted sensor, is identical with the axis of symmetry of the sensor'sviewing zone 7. This is also the principal beam direction of thesensor's radiation characteristic. Rays 6 and 10 represent the right andleft edges, respectively, of the sector-shaped sensor viewing zone, ray8 being exactly the bisector of the two rays 6 and 10. The lines markingan accurately adjusted sensor region (6, 8, 10) are indicated in FIG. 1by solid lines. In the case of a horizontally misaligned sensor, i.e.,the misalignment of the radiation characteristic was ascertained asbeing not equal to zero, the sensor's viewing zone is illustrated bybroken lines 5, 7 and 9. These rays differ from rays 6, 8 and 10 only inthat they are rotated by the horizontal misalignment angle theta, asillustrated in FIG. 1. In this regard, ray 5 represents the right edgeof the sensor's viewing zone and ray 9 represents the left edge of thesensor's viewing zone. Ray 7 is the bisector between rays 5 and 9, andthus the center axis of the sector-shaped viewing zone of the sensor.Angle theta 11 indicates the sensor misalignment rotation. This anglemay be measured between the motor vehicle's center axis and the axis ofsymmetry of the sensor's viewing zone. Inside the viewing zone of thesensor, an electromagnetic wave is emitted, e.g., a radar or LIDARsignal. Objects present in this viewing zone of the sensor scatter backa reflected wave which is detected at the sensor with the correspondingpropagation delay. The angle at which a reflected signal is radiated andreceived is designated as the object angle, and is processed further asobject angle value. All objects within the sensor's viewing zone areknown by object distance and object angle. From these objects, a targetobject is selected. The object being selected may closest in distanceand closest to the vicinity of the longitudinal axis of the vehicle.

FIG. 2 is a two-dimensional diagram illustrating the switch-off range aswell as the functional range. The two coordinate axes 12 and 13 form anorthogonal system. The instantaneous misalignment value of one of thetwo individual procedures is plotted on each axis, whereby themisalignment value combination of the instantaneous individualmisalignment values may be represented by a point in two-dimensionalerror space. In this example embodiment, the normalized error of thelong-term filtering of the target object's course displacement isplotted on coordinate axis 12. The normalization occurs in such a waythat the maximum tolerable error d_alpha_obj_max of this method ismarked by point 14. Analogously, the normalized misalignment value ofthe regression analysis of trajectories is plotted on coordinate axis13. Normalization occurs in the same manner, so that the maximumtolerable misalignment value of this method, d_alpha_traj_max is markedby point 15. If both methods for misalignment recognition are evaluatedseparately from each other, the evaluations yield a rectangle the centerof which corresponds to the coordinate's origin. If the instantaneousmisalignment point is inside this rectangle, this indicates that bothsingle errors simultaneously are below each of their limiting values.One may then assume that the misalignment values arise throughnon-optimal travel situations, and the sensor's viewing zone may bereadjusted. One may combine both methods with each other. If bothmethods indicate errors having the same sign, this indicates that theerror points are in quadrants I or III, and if possibly they also lienear straight line 16, then both methods detect approximately the samemisalignment value, and, with greater probability than with the use ofone individual procedure, one may assume actual determination of theradiation characteristic compared to the vehicle's longitudinal axis.Because of this, in these areas, that is, in quadrants I and III, onemay limit the functional region by removing a part of the functionalregion. This region, which now belongs to the switching off region, isthus called “broadened switching off region”.

It should be noted that the borders between functional region andswitching off region 17, as well as between functional region andbroadened switching off region 18, as well as between switching offregion and broadened switching off region 19 are illustrated in all fourquadrants in FIG. 2 as straight lines, for simplicity, but in practicethey may be shaped as any desired curves.

One may introduce further “broadened switching off regions”, so as to beable to model the border of the functional region or the functionalregions, as the case may be, as desired.

The functional manner of this combination method is illustrated in FIG.3. The two single procedures “long-term filtering of the target object'stravel-path misalignment” 20 as well as “regression analysis oftrajectories” 21 calculate in each case an instantaneous misalignmentvalue d_alpha_obj or d_alpha_traj. These two values are passed on tofunction blocks 24, 25 and 26, as in FIG. 3.

The travel situation is simultaneously ascertained from measured traveldynamics of other systems and/or additional vehicle data. In thisconnection, it is determined whether the vehicle is traveling straightahead or along a curve, whether it is going upwardly or downwardly, orwhether further conditions impairing the measuring procedures arefulfilled, e.g., in that a yaw rate signal, a pitch signal or additionalsignals describing travel dynamics are used. From the ascertained travelsituation, a quality factor is calculated for each procedure in functionblock 22. The quality factor for the long-term filtering of the targetobject travel path displacement is passed on as q_obj, and the qualityfactor for the regression analysis of trajectories is passed on asq_traj. These quality factors are passed on to blocks 24, 25 and 26 insuch a way that block 25 receives both quality factors q_obj and q_traj,block 24 only receives q_obj and block 26 only receives q_traj. In block25, the broadened switching off region is now formed using the function

F 3(d_alpha_obj, q_obj, d_alpha_traj, q_traj)> . . . K1(d_alpha_obj_max, _alpha_traj_max)

the two misalignment values d_alpha_obj and d_alpha_traj being weightedwith the aid of quality factors q_obj and q_traj. If this equation issatisfied, then a greater error is present than is permissible, and aswitching off request is passed on to block 27.

In block 24, using single misalignment value d_alpha_obj and therespective quality factor q_obj, a test is made whether

F 1(d_alpha_obj, q_obj)>q_alpha_obj_max

is satisfied. If yes, the error is greater than is permissible, and theswitching off request is passed on to block 27. In block 26, usingsingle misalignment value d_alpha_traj and the respective quality factorq_traj, a test is made whether the condition

F 2(d_alpha_traj, q_traj)>q_alpha_traj_max

is satisfied. If yes, the error is greater than is permissible, and theswitching off request is passed on to block 27. If block 27 receives atleast one switching off request from one of blocks 24, 25 or 26, it ispassed on to block 29 that the proximity-control system and the cruisecontrol may be switched off.

In FIG. 4 a further example embodiment of the present invention isillustrated. This example embodiment includes all the parts described inFIG. 3, but with additional supplementations. Block 24 has been added.Block 23 receives the two single misalignment values d_alpha_obj andd_alpha_traj as well as the pertaining quality factors q_obj and q_traj.In block 23, a linked misalignment value d_alpha_comb is formed fromthese values, using the single misalignment values. The value thuscreated, d_alpha_comb is then passed on to likewise newly added block 28where correction of the main radiation direction of the radiationcharacteristic is performed. If function block 28 is informed of arequest to switch off, it causes deactivation of the correction and alsodeactivates the entire proximity-control system and cruise controlsystem.

The values d_alpha_obj_max as well as d_alpha_traj_max may be constantvalues, but they may also be functions as illustrated in FIG. 2 asarbitrary straight lines, or they may look like arbitrarily shapedcurves.

A plurality of variants are possible during system deactivation. Thusswitching off the vehicle control may be kept up only so long asmisalignment values are in a correctable region, that is, that block 27receives at least one switching off request, or it may be switched offuntil the vehicle is started the next time and a negative self-diagnosishas been performed, or again, deactivation is kept up until this errormessage, which is stored in a nonvolatile memory, is reset in a garage.

The correction of the sensor's viewing zone may also be made in adifferent manner. One possibility is to add the determined linkedmisalignment angle value to all measured angle values, so that the newsensor viewing zone is tilted by calculation into the correct position.Another possibility provides for displacing the edge of the sensorviewing zone, which is on the side in the direction of which the axis ofsymmetry of the viewing zone has been displaced toward the center, untilthe axis of symmetry of the sensor's viewing zone is identical to thevehicle's center axis. This may have the disadvantage that the sensor'sviewing zone becomes less at each correction, and after some operatingperiod no longer exists.

In addition to monitoring the sensor adjustment, one may also monitorthe sensor hardware. With certain combinations of the singlemisalignment values (d_alpha_obj; d_alpha_traj) one may conclude, onaccount of experiences gathered, that there are special defects in thesensor's hardware. If these combinations arise, the regulating systemmust be switched off due to possible hardware defects.

By linking a plurality of procedures, it is possible on the one hand todetermine with greater probability that the ascertained correction valuecorresponds to the actual sensor malposition than when using a singleprocedure, whereby a robust monitoring procedure is ensured, andfurthermore it is also possible to monitor parts of the sensor hardwarefor their functioning.

What is claimed is:
 1. A method for ascertaining an alignment error of aradiation characteristic of a sensor for a cruise control and aproximity control system of a vehicle with respect to a vehiclelongitudinal axis, comprising the steps of: ascertaining the alignmenterror in accordance with at least two differently defined singleprocedures; linking single misalignment values of the single procedureswith each other to form a linked misalignment value; and switching offthe cruise control and proximity control system when one of thefollowing conditions is satisfied: a first value, which is determinedfrom the single misalignment values and quality factors, is greater thana first limiting value, wherein each of the quality factors correspondsto one of the single misalignment values, and one of the singlemisalignment values of the single procedures is greater than a secondlimiting value, wherein the one of the single misalignment values isweighted by a quality factor.
 2. The method according to claim 1,further comprising the steps of: recording an instantaneously presenttravel state; and ascertaining the linked misalignment value inaccordance with the instantaneously present travel state.
 3. The methodaccording to claim 2, wherein the linked misalignment value ascertainingstep includes the substep of weighting the misalignment values of thesingle procedures using quality factors formed from the instantaneoustravel state.
 4. The method according to claim 1, wherein a first one ofthe single procedures is configured so that a misalignment value isascertained on the basis of a mean value generation in time via aninstantaneous target object angle to a vehicle center axis; and whereina second one of the single procedures is configured so that a furthermisalignment value is ascertained using a trajectories method, thetrajectories method including the substeps of: recognizing a relativechange in an object position in accordance with a vehicle speed; andascertaining a lateral relative speed of the object with respect to thevehicle center axis in accordance with the relative change of the objectposition.
 5. The method according to claim 4, wherein the objectincludes a standing backscattering object.
 6. The method according toclaim 1, further comprising the step of continuously correcting theradiation characteristic of the sensor with respect to the vehiclelongitudinal axis by the linked misalignment value.
 7. The methodaccording to claim 1, further comprising the steps of: deactivating thecruise control and proximity control system when one of the limitingvalues is exceeded; and preventing reactivation of the cruise controland proximity control system until one of: the misalignment values ofthe single procedures and the linked misalignment value are within apermissible error region; an ignition of the vehicle is switched onagain and a self-diagnosis without findings has been performed; and adeactivation state stored by the cruise control and proximity controlsystem in a non-volatile manner is canceled.
 8. The method according toclaim 1, further comprising the step of continuously correcting a mainpropagation direction of the radiation characteristic by one of: tiltingthe radiation characteristic by addition of the linked misalignmentvalue to measured object angle values so that the main propagationdirection coincides with the vehicle longitudinal axis; and displacing alateral boundary of a sector-shaped radiation characteristic, in adirection of which the main propagation direction is displaced from thevehicle longitudinal axis toward a center until a sensor viewing zone isnarrowed to be symmetrical with respect to the vehicle longitudinalaxis.
 9. The method according to claim 1, further comprising the step ofinferring a special defect in the sensor hardware in accordance withcertain combinations of at least one of the misalignment values of thesingle procedures and the quality factors.
 10. The method according toclaim 1, wherein the first limiting value is determined from a firstpredefined misalignment value and a first predefined quality factorvalue.
 11. The method according to claim 1, wherein the second limitingvalue is determined from a second predefined misalignment value and asecond predefined quality factor value.
 12. The method according toclaim 1, wherein the first limiting value is determined from a firstpredefined misalignment value and a first predefined quality factorvalue, and wherein the second limiting value is determined from a secondpredefined misalignment value and a second predefined quality factorvalue.
 13. The method according to claim 1, wherein one of the singlemisalignment values is based on a travel path displacement, and anotherof the single misalignment values is based on a trajectory.
 14. Themethod according to claim 1, wherein one of the single misalignmentvalues is based on a travel path displacement.
 15. The method accordingto claim 1, wherein one of the single misalignment values is based on atrajectory.
 16. A device for ascertaining an alignment error of aradiation characteristic of a sensor for cruise control and proximitycontrol of a vehicle with respect to a vehicle longitudinal axis,comprising: an arrangement configured to ascertain the alignment errorin accordance with at least two differently defined single procedures;an arrangement configured to link misalignment values of the singleprocedures together to form a linked misalignment value; an arrangementconfigured to switch off the cruise control and proximity control systemas a function of the linked misalignment value; and an arrangement torecord an instantaneously present travel state and to form therefromquality factors, to link misalignment values of the single procedures,and to ascertain the linked misalignment value in accordance with thequality factors.
 17. The device according to claim 16, wherein thearrangement to link misalignment values is operable to weight themisalignment values of the single procedures in accordance with thequality factors.